I had cleanly unmountzed an USB memory stick via file manager, then unplugged
it.
After that I noticed that the system is unresponsive. Soon after window
decorations vanished from my windows, and CPU load was very high (seeing three
systemd-coredump processes taking 100% CPU each). Then the whole GNOME session
was aborted. I needed two attempts to reestablish a new GNOME session.

Unfortunately there are no good logs, and I couldn't find the cores.
gnome-shell-3.20.4-8.1.x86_64

Mar 24 09:24:26 pc packagekitd[21536]: (packagekitd:21536): GLib-CRITICAL **:
Source ID 15 was not found when attempting to remove it
Mar 24 09:24:30 pc dbus[1340]: [system] Failed to activate service 'org.bluez':
timed out
Mar 24 09:24:30 pc pulseaudio[21504]: [pulseaudio] bluez5-util.c:
GetManagedObjects() failed: org.freedesktop.DBus.Error.NoReply: Did not receive
a reply. Possible causes include: the remote application did not send a reply,
the message bus security policy blocked the reply, the reply timeout expired,
or the network connection was broken.
Mar 24 09:24:31 pc systemd-coredump[20814]: Process 20787 (gnome-shell) of user
1000 dumped core.
## I started to investigate:
Mar 24 09:24:32 pc login[1397]: pam_unix(login:session): session opened for
user root by LOGIN(uid=0)

Mar 24 09:25:20 pcrz00066 systemd-coredump[21355]: Process 21145 (gnome-shell)
of user 1000 dumped core.
Mar 24 09:26:20 pcrz00066 systemd-coredump[21408]: Process 21356 (gnome-shell)
of user 1000 dumped core.
Mar 24 09:27:49 pcrz00066 systemd-coredump[20783]: Process 2665 (gnome-shell)
of user 1000 dumped core.